As Part I opens, Antoinette Cosway is a young girl living with her mother and brother at Coulibri, her family's estate near Spanish Town, Jamaica. With the passage of the Emancipation Act and the death of her father, the family is financially ruined. Moreover, they are ostracized by both the black and white communities on the island. The black community despises them for being former slaveholders, and the white community looks down on them because they are poor, Creole, and, in her mother's case, French. Among the only servants who remain is Christophine, a Martinique woman who is rumored to practice obeah.
Motivated in part by her family's desperate situation, Annette, Antoinette's mother, marries Mr. Mason, a wealthy planter. This marriage, however, only seems to aggravate racial tensions in their neighborhood. One night, rioters burn the house down. The entire family narrowly escapes, all except Antoinette's brother Pierre, who, due to his exposure to the smoke, either dies very soon after. Pierre's death devastates Annette, who goes mad with grief. Mr. Mason sends Annette off to an isolated house to be cared for by a couple of color. Antoinette is sent to live with her aunt Cora in Spanish Town. For a year and a half, Antoinette attends a convent school there. Part I ends with Mr. Mason back in Antoinette's life, insinuating that plans for arranging her marriage are already under way.
Part II opens with a newly wedded Antoinette and Rochester on their honeymoon in Granbois, the Cosway estate outside Massacre, Dominica. Through a series of flashbacks, we learn that their marriage was arranged by Rochester's father, Mr. Mason, and Richard Mason, Antoinette's stepbrother. After only a month of courtship, Rochester married Antoinette. While at first wary of each other, Antoinette and Rochester grow to trust each other and consummate their marriage.
But the honeymoon is short-lived, as Rochester receives a malicious letter from a man who claims to be Daniel Cosway, Antoinette's stepbrother. The letter alleges that there is a history of sexual degeneracy and mental illness in Antoinette's family, and it also alleges that Antoinette had previously been engaged to a relative of color, Sandi Cosway. After receiving the letter, Rochester spurns Antoinette. Using an obeah potion obtained from Christophine, Antoinette drugs and seduces Rochester. On waking, Rochester realizes that he has been drugged, and sleeps with Antoinette's maid in revenge. Betrayed, Antoinette seems to go mad herself. Part II ends with their departure from Granbois to Spanish Town, where Rochester plans to have Antoinette declared insane and confined.
Part III opens with Antoinette already confined in Thornfield Hall (in England), guarded by Grace Poole. Antoinette seems to have little sense of who or where she is at this point. Her stepbrother Richard Mason visits her, and she attacks him after he refuses to help her out of her marriage. Finally, she dreams that she escapes from her room and sets fire to the entire house. At the end of the dream, she flees to the top of the battlements, then jumps off. Antoinette wakes up, and the novel ends as she escapes from her room, with a candle lighting her way down a dark hallway.